In general, an optical module refers to a module in which various optical communication functions are collected in one package to be connected with an optical fiber. Recently, a bi-directional optical module, in which an optical transmitter using a laser diode, which has low power consumption and is utilizable for a long distance, as a light source, and an optical receiver performing optical communication by using a photodiode are modulated into one module, is mainly used.
The bi-directional optical module includes an optical transmitter, an optical receiver, an optical filter, an optical fiber, a holder for accommodating the optical fiber, and the like. A first optical signal (incident light) output from the optical fiber is reflected by the optical filter to be incident to the optical receiver, and a second optical signal (output light) output from the optical transmitter passes through the optical filter to be incident to the optical fiber.
The optical filter is generally disposed while being inclined at 45° to separate the first optical signal and the second optical signal, but when a wavelength interval between the first optical signal and the second optical signal is 60 nm or lower, particularly, in an environment at −40° C. to 85° C., it is impossible to separate the optical signals according to a property of the filter.